Bootstrap模态在切换，后台滚动时不变为活动元素，但模态不滚动

Question

I have a web page that makes use of a number of different modals to display information to the user.

These modals are triggered by certain buttons, which usually call $("#id").modal("toggle") to toggle the modal's visibility on. In one particular scenario, I have one modal which displays a second modal through the use of the above stated function. It also hides itself through the use of the same function, so I have an onClick function that does the following.

$("#EditTask").modal("hide");
$("#AddressProspect").modal("show");

The issue is that when the AddressProspect modal is displayed, it seems as though it is not being changed to the active element. The background goes dark, and the modal is displayed correctly. However when I attempt to scroll, the background elements scroll instead, as if the modal hasn't actually been displayed.

I have attempted a number of different approaches. I have used .modal("show") and .modal("hide") to display the modals I need. I have also tried .modal("hide") to display the modals I need. I have also tried data-dismiss="modal" within the button of the modal that needs to be hidden. These have all produced the exact same result.

Interestingly, if I go to my console and execute the following commands

$("body").css("overflow-y", "hidden");
$("#AddressProspect").css("overflow-y", "scroll");

The background becomes unscrollable, and the AddressProspect modal becomes scrollable, just as I would expect.

I have around 10 modals being used within my page, and none of them have this problem apart from the one in question. I have posted the code to the two modals mentioned in this post below, with their bodies removed for clarity.

<div class="modal fade bd-example-modal-lg" id="EditTask" tabindex="-1" role="dialog" data-keyboard="false" data-backdrop="static" aria-labelledby="exampleModalLabel" aria-hidden="true">
    <div class="modal-dialog modal-lg" role="document">
        <div class="modal-content">
            <div class="modal-header">
                <h5 class="modal-title" id="exampleModalLabel"><span class="Title">Title</span></h5>
                <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                    <span aria-hidden="true">&times;</span>
                </button>
            </div>
            <div class="modal-body">

                    -snip-

            </div>
            <div class="modal-footer">
                <div style="width: 100%">
                    <button type="button" class="btn btn-warning action-skip-instruction" style="float: left;" data-dismiss="modal">Skip Instruction</button>
                </div>

                <button type="button" class="btn btn-secondary action-close-edit-modal">Close</button>
                <button type="button" id="edit-task-button-defer" class="btn btn-warning edit-task-action" style="display: none;">Defer</button>
                <button type="button" id="edit-task-button-action" class="btn btn-success edit-task-action" data-dismiss="modal">Complete</button>

            </div>
        </div>
    </div>
</div>

<div class="modal fade" id="AddressProspect" tabindex="-1" role="dialog" data-keyboard="false" data-backdrop="static" aria-labelledby="exampleModalLabel" aria-hidden="true">
        <div class="modal-dialog" style="max-width: 600px;" role="document">
            <div class="modal-content">
                <div class="modal-header">
                    <h5 class="modal-title">New Security Address Prospect</h5>
                </div>

                <div class="modal-body">

                    -snip-

                </div>
                <div class="modal-footer">
                    <div style="width: 100%">
                        <button type="button" class="btn btn-warning prospect-button-clear" style="float: left;">Clear</button>
                    </div>

                    <button type="button" style="float: left;" class="btn btn-danger prospect-button-close" data-dismiss="modal">Close</button>
                    <button type="button" class="btn btn-success prospect-button-update">Update</button>
                </div>
            </div>
        </div>
    </div>

Answer 1

After a decent amount of time having issues with this problem I have managed to figure out why it is happening and how to fix it.

There are two places I looked for information on this topic:

This Github issue on the Bootstrap repo

The Bootstrap documentation on modal methods

From reading the Github issue we can see that one user notes that the calls to .modal("hide") and .modal("show") are asynchronous, therefore using them in quick succession is invalid. Instead we must wait for the show/hide to complete by listening for the shown or hidden events.

To do this we can use the following function:

$('#myModal').on('hidden.bs.modal', function (e) {
  // do something...
})

By checking for the hidden.bs.modal class to be placed into the modal's classlist we can verify when the hide animation has completely finished. At this point we can then call the show method of the next modal to be displayed, ensuring that all of the background events handled by Bootstrap have finished executing, and ensuring that behaviour is expected.

My previous code goes from being:

$("#EditTask").modal("hide");
$("#AddressProspect").modal("show");

to:

$("#EditTask").modal('toggle');
$("#EditTask").on("hidden.bs.modal", function() {
      $("#AddressProspect").modal('toggle');        
      });

As soon as I tried the new code, the weird issues with scrolling disappeared.